In order to conduct communications with a satellite, the location of which can be expected to vary (sometimes very substantially) relative to a (mobile) platform's antenna boresight axis, reduced hardware complexity communication platforms often employ helical antennas, such as the monofilar winding structure, diagrammatically shown at 10 in FIG. 1. Although the reduced complexity of a conventional monofilar antenna makes it a relatively inexpensive structure, it's radiation pattern is concentrated along the (boresight) axis 12 of the helical winding; as a result, the pattern cannot be effectively scanned, so that it has limited phased array utility.
In order to maintain communication connectivity with a satellite, it is preferred that antennas not only be capable of being scanned, but have proper polarization. Where circular polarization is desired, the helical antenna has been typically configured as a multi-winding structure, as diagrammatically illustrated in FIG. 2, comprised of a plurality of concentrically arranged helical windings 13, each having a fractional number of turns, and terminating the respective windings to a multi-quadrature port hybrid interface 14.
A drawback to this conventional multi-winding architecture is the cost and hardware complexity of the combination of the antenna proper and its electronic interface. For the conventional monofilar structure shown in FIG. 1, the gain pattern 20 of such an antenna exhibits a substantial lobe along and in the close vicinity of the boresight axis 12, making the antenna effectively an `axial mode` device. As a result, it is not well suited for wide beam coverage, particularly since increasing the number of turns of each winding in order to enhance its circular polarization characteristics also increases the gain of the helical winding along its longitudinal (boresight) axis.